[PATCH v4 1/4] drm: rework description of primary and cursor planes

[PATCH v4 1/4] drm: rework description of primary and cursor planes

[Simon Ser]

The previous wording could be understood by user-space evelopers as "a
primary/cursor plane is only compatible with a single CRTC" [1].

Reword the planes description to make it clear the DRM-internal
drm_crtc.primary and drm_crtc.cursor planes are for legacy uAPI.

[1]: https://github.com/swaywm/wlroots/pull/2333#discussion_r456788057

Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
---
 drivers/gpu/drm/drm_crtc.c  |  3 +++
 drivers/gpu/drm/drm_plane.c | 16 +++++++++-------
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 8d19d258547f..a6336c7154d6 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -256,6 +256,9 @@ struct dma_fence *drm_crtc_create_fence(struct drm_crtc *crtc)
  * planes). For really simple hardware which has only 1 plane look at
  * drm_simple_display_pipe_init() instead.
  *
+ * The @primary and @cursor planes are only relevant for legacy uAPI, see
+ * &drm_crtc.primary and &drm_crtc.cursor.
+ *
  * Returns:
  * Zero on success, error code on failure.
  */
diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index 385801dd21f9..5d33ca9f0032 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -49,14 +49,16 @@
  * &struct drm_plane (possibly as part of a larger structure) and registers it
  * with a call to drm_universal_plane_init().
  *
- * Cursor and overlay planes are optional. All drivers should provide one
- * primary plane per CRTC to avoid surprising userspace too much. See enum
- * drm_plane_type for a more in-depth discussion of these special uapi-relevant
- * plane types. Special planes are associated with their CRTC by calling
- * drm_crtc_init_with_planes().
- *
  * The type of a plane is exposed in the immutable "type" enumeration property,
- * which has one of the following values: "Overlay", "Primary", "Cursor".
+ * which has one of the following values: "Overlay", "Primary", "Cursor" (see
+ * enum drm_plane_type). A plane can be compatible with multiple CRTCs, see
+ * &drm_plane.possible_crtcs.
+ *
+ * Legacy uAPI doesn't expose the primary and cursor planes directly. DRM core
+ * relies on the driver to set the primary and optionally the cursor plane used
+ * for legacy IOCTLs. This is done by calling drm_crtc_init_with_planes(). All
+ * drivers should provide one primary plane per CRTC to avoid surprising legacy
+ * userspace too much.
  */
 
 static unsigned int drm_num_planes(struct drm_device *dev)
-- 
2.29.2

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[PATCH v4 2/4] drm: validate possible_crtcs for primary and cursor planes

[Simon Ser]

If a primary or cursor plane is not compatible with a CRTC it's attached
to via the legacy primary/cursor field, things will be broken for legacy
user-space.

v4: use drm_crtc_mask instead of BIT (Ville)

Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/drm_mode_config.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index f1affc1bb679..1628c8b60d9a 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -625,6 +625,7 @@ static void validate_encoder_possible_crtcs(struct drm_encoder *encoder)
 void drm_mode_config_validate(struct drm_device *dev)
 {
 	struct drm_encoder *encoder;
+	struct drm_crtc *crtc;
 
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		return;
@@ -636,4 +637,19 @@ void drm_mode_config_validate(struct drm_device *dev)
 		validate_encoder_possible_clones(encoder);
 		validate_encoder_possible_crtcs(encoder);
 	}
+
+	drm_for_each_crtc(crtc, dev) {
+		if (crtc->primary) {
+			WARN(!(crtc->primary->possible_crtcs & drm_crtc_mask(crtc)),
+			     "Bogus primary plane possible_crtcs: [PLANE:%d:%s] must be compatible with [CRTC:%d:%s]\n",
+			     crtc->primary->base.id, crtc->primary->name,
+			     crtc->base.id, crtc->name);
+		}
+		if (crtc->cursor) {
+			WARN(!(crtc->cursor->possible_crtcs & drm_crtc_mask(crtc)),
+			     "Bogus cursor plane possible_crtcs: [PLANE:%d:%s] must be compatible with [CRTC:%d:%s]\n",
+			     crtc->cursor->base.id, crtc->cursor->name,
+			     crtc->base.id, crtc->name);
+		}
+	}
 }
-- 
2.29.2

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[PATCH v4 3/4] drm: require a non_NULL drm_crtc.primary

[Simon Ser]

If a CRTC is missing a legacy primary plane pointer, a lot of things
will be broken for user-space: fbdev stops working and the entire legacy
uAPI stops working.

Require all drivers to populate drm_crtc.primary to prevent these
issues. Warn if it's NULL.

Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
---
 drivers/gpu/drm/drm_mode_config.c | 3 +++
 drivers/gpu/drm/drm_plane.c       | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index 1628c8b60d9a..1e5da83fd2a8 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -639,6 +639,9 @@ void drm_mode_config_validate(struct drm_device *dev)
 	}
 
 	drm_for_each_crtc(crtc, dev) {
+		WARN(!crtc->primary, "Missing primary plane on [CRTC:%d:%s]\n",
+		     crtc->base.id, crtc->name);
+
 		if (crtc->primary) {
 			WARN(!(crtc->primary->possible_crtcs & drm_crtc_mask(crtc)),
 			     "Bogus primary plane possible_crtcs: [PLANE:%d:%s] must be compatible with [CRTC:%d:%s]\n",
diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index 5d33ca9f0032..49b0a8b9ac02 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -57,7 +57,7 @@
  * Legacy uAPI doesn't expose the primary and cursor planes directly. DRM core
  * relies on the driver to set the primary and optionally the cursor plane used
  * for legacy IOCTLs. This is done by calling drm_crtc_init_with_planes(). All
- * drivers should provide one primary plane per CRTC to avoid surprising legacy
+ * drivers must provide one primary plane per CRTC to avoid surprising legacy
  * userspace too much.
  */
 
-- 
2.29.2

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[PATCH v4 4/4] drm: require each CRTC to have a unique primary plane

[Simon Ser]

User-space expects to be able to pick a primary plane for each CRTC
exposed by the driver. Make sure this assumption holds in
drm_mode_config_validate.

Use the legacy drm_crtc.primary field to check this, because it's
simpler and we require drivers to set it anyways. Accumulate a set of
primary planes which are already used for a CRTC in a bitmask. Error out
if a primary plane is re-used.

v2: new patch

v3:
- Use u64 instead of __u64 (Jani)
- Use `unsigned int` instead of `unsigned` (Jani)

v4:
- Use u32 instead of u64 for plane mask (Ville)
- Use drm_plane_mask instead of BIT (Ville)
- Fix typos (Ville)

Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Cc: Pekka Paalanen <ppaalanen@gmail.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/drm_mode_config.c | 21 +++++++++++++++++++++
 drivers/gpu/drm/drm_plane.c       |  6 ++++++
 2 files changed, 27 insertions(+)

diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index 1e5da83fd2a8..7ffc0d6a8e2c 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -626,6 +626,9 @@ void drm_mode_config_validate(struct drm_device *dev)
 {
 	struct drm_encoder *encoder;
 	struct drm_crtc *crtc;
+	struct drm_plane *plane;
+	u32 primary_with_crtc = 0, cursor_with_crtc = 0;
+	unsigned int num_primary = 0;
 
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		return;
@@ -647,12 +650,30 @@ void drm_mode_config_validate(struct drm_device *dev)
 			     "Bogus primary plane possible_crtcs: [PLANE:%d:%s] must be compatible with [CRTC:%d:%s]\n",
 			     crtc->primary->base.id, crtc->primary->name,
 			     crtc->base.id, crtc->name);
+			WARN(primary_with_crtc & drm_plane_mask(crtc->primary),
+			     "Primary plane [PLANE:%d:%s] used for multiple CRTCs",
+			     crtc->primary->base.id, crtc->primary->name);
+			primary_with_crtc |= drm_plane_mask(crtc->primary);
 		}
 		if (crtc->cursor) {
 			WARN(!(crtc->cursor->possible_crtcs & drm_crtc_mask(crtc)),
 			     "Bogus cursor plane possible_crtcs: [PLANE:%d:%s] must be compatible with [CRTC:%d:%s]\n",
 			     crtc->cursor->base.id, crtc->cursor->name,
 			     crtc->base.id, crtc->name);
+			WARN(cursor_with_crtc & drm_plane_mask(crtc->cursor),
+			     "Cursor plane [PLANE:%d:%s] used for multiple CRTCs",
+			     crtc->cursor->base.id, crtc->cursor->name);
+			cursor_with_crtc |= drm_plane_mask(crtc->cursor);
 		}
 	}
+
+	drm_for_each_plane(plane, dev) {
+		if (plane->type == DRM_PLANE_TYPE_PRIMARY) {
+			num_primary++;
+		}
+	}
+
+	WARN(num_primary != dev->mode_config.num_crtc,
+	     "Must have as many primary planes as there are CRTCs, but have %u primary planes and %u CRTCs",
+	     num_primary, dev->mode_config.num_crtc);
 }
diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index 49b0a8b9ac02..a1f4510efa83 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -54,6 +54,12 @@
  * enum drm_plane_type). A plane can be compatible with multiple CRTCs, see
  * &drm_plane.possible_crtcs.
  *
+ * Each CRTC must have a unique primary plane userspace can attach to enable
+ * the CRTC. In other words, userspace must be able to attach a different
+ * primary plane to each CRTC at the same time. Primary planes can still be
+ * compatible with multiple CRTCs. There must be exactly as many primary planes
+ * as there are CRTCs.
+ *
  * Legacy uAPI doesn't expose the primary and cursor planes directly. DRM core
  * relies on the driver to set the primary and optionally the cursor plane used
  * for legacy IOCTLs. This is done by calling drm_crtc_init_with_planes(). All
-- 
2.29.2

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